[RCU] Login failed

Hi,
strange thing!! I uploaded some days again my version of roundcube, and everything was working, I could connect to any IMAP server. But since today my login fail but without an error (mit log status is 4, so errors should be displayed), if I log in with a wrong password there will be an error displayed.
Check this out: http://jangloeckner.virtual.vps-host.net/roundcube/
Exactly the same roundcube configuration runs on an other server, there everything is working fine (check it out: http://www.dddesign.ch/roundcube/ )
Any ideas?
jan
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